This invention pertains to skeletal iron catalyst and its preparation and use in Fischer-Tropsch and similar slurry-phase synthesis processes. More particularly, such skeletal iron catalyst utilized in slurry phase synthesis processes for H.sub.2 +CO feedstreams has increased attrition resistance and improved catalyst/product liquid separation, while providing increased selectivity for producing C.sub.2 -C.sub.5 light olefin products.
Slurry phase Fischer-Tropsch (F-T) synthesis process technology is an important known route for indirect coal liquefaction for synthesis of liquid fuels from H.sub.2 +CO feedstreams. Precipitated iron is currently a commonly used catalyst for such Fischer-Tropsch processes. However, precipitated iron catalysts are undesirably fragile and break down easily under reaction conditions into very fine particles, so that separation of such fine catalyst particles from reaction product waxes is difficult to accomplish and results in inferior product quality and significant catalyst loss. Such catalyst problems hinders commercial use of the process. For overcoming this problem, improved skeletal iron catalysts made according to this invention are provided by utilizing caustic extraction and/or leaching non-ferrous metals from specific iron metal alloy particles, and such skeletal iron catalysts have good particle strength and attrition resistance. Literature studies on such catalysts to date have focused on improvement of catalyst activity in simple gas-solid hydrogenation reaction system. Utilization of such improved skeletal iron catalyst in slurry-phase or three-phase gas-liquid-solid Fischer-Tropsch reaction processes fully realizes the advantages of such skeletal iron catalysts. By utilizing such improved skeletal iron catalysts, commercial slurry-bed Fischer-Tropsch synthesis to produce clean hydrocarbon transportation fuels from syngas feedstreams is greatly facilitated.
Light olefins C.sub.2 - to C.sub.5 - are key component materials in the petrochemical industry as important feedstocks and building blocks for the synthesis of a variety of chemical/petrochemical products. Conventionally, such light olefins are produced by thermal cracking of hydrocarbons ranging from ethane to vacuum gas oils, but not produced directly from natural gas which is essentially methane (CH.sub.4). Such thermal cracking is practiced under high temperatures (1,500-1,600.degree. F.), thus requiring costly construction materials and consuming huge amounts of energy for feedstream heating and reaction. A commercially practiced technical route for making light olefins from natural gas is to first convert natural gas via steam reforming into a mixture of hydrogen and carbon monoxide, called synthesis gas or syngas. The current technology of converting syngas into olefins is a two-step catalytic conversion, the first step being catalytic conversion of syngas to methanol, followed by conversion of methanol into olefins. A unique catalyst/technology would be to directly convert synthesis gas into light olefins, without the necessity of an additional step for making methanol as an intermediate material. The skeletal iron catalyst, promoted with other metal ingredients and used in a fixed bed or in slurry-bed reactor system with liquid paraffin as the liquid medium, can advantageously convert syngas directly into light olefins C.sub.2 --C.sub.5 - under mild conditions in a temperature range of 180-350.degree. C. and a pressure range of 0.5-5.0 mPa.
Thus, this invention provides a unique skeletal iron catalyst having high activity for catalyzing the conversion of syngas feeds to a broad range of hydrocarbon products, and has high selectivity towards light olefins formation in a slurry-phase catalytic reactor system under mild conditions conventionally used in Fischer-Tropsch synthesis, so that the hydrocarbon product is rich in olefins.